Abstract
AbstractThe detection of molecules dissolved in liquid medium can be envisaged by means of an optical integrated sensor operating in middle infrared range. The intended sensor is composed of a cladding and a guiding selenide sputtered layers transparent in middle infrared. Hence, Ge-Sb-Se thin films were selected in view of tailored refractive index contrast, successfully deposited by radio frequency magnetron sputtering and characterized. To maximize the evanescent field at a wavelength of 7.7 µm, a suitable selenide waveguide allowing measuring the optical transmitted power was designed by performing computer simulations based on the effective index method enabling single-mode propagation for a waveguide width between 8 and 12 µm. Selenide sputtered films were micro-patterned using reactive ion etching with inductively coupled plasma process. Finally, optical waveguide surface was functionalized by the deposition of a hydrophobic polymer, which will permit detection of organic molecules in water.
Highlights
The development of sensor enabling in situ detection of organic molecules in water by means of optical method is a vast ecological challenge [1,2]
Ge28.1Sb6.3Se65.6 (x = 10) and Ge12.5Sb25Se62.5 (x = 50), were selected for this aim. The fabrication of these two distinct selenide films has been optimized by the experimental design approach in order to fully meet the criteria for producing optical components devoted to optical biochemical sensor applications, for which controlling the layer homogeneity is fundamental for thicknesses of few μm
The chemical composition of chalcogenide targets is in good agreement with the theoretical composition and the Ge28.1Sb6.3Se65.6 and Ge12.5Sb25Se62.5 sputtered thin films deposited under 1·10−2 mbar Ar pressure are relatively close to the nominal composition of target with an excess in germanium, 3·9 and 2·2 at. % and a ADVANCED DEVICE MATERIALS 25 deficit can be noted, 3·7 and 2·2 at. % in the case of selenium
Summary
The development of sensor enabling in situ detection of organic molecules in water by means of optical method is a vast ecological challenge [1,2]. Among the various categories of optical sensor including the conventional attenuated total reflectance (ATR), the detection by means of evanescent field is one of the possible ways to allow the miniaturization of the sensor device with integration of mid-infrared photonic components and lowcost production [6]. Concerning, the optical platform -the key-stone of the sensor-, while other mid-IR platforms have been investigated lately, such as germanium (Ge) [8] and gallium arsenide (GaAs) [9], chalcogenide glasses has attracted attention for sensing applications due to their wide transparency in the infrared range [1,14], their ability to be fabricated in thin film by PVD and manufactured into integrated photonic components by photolithographic and etching process.
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